Heretofore canned foods of fish flakes have been produced by way of boiling fish such as tuna, bonito and mackerel, removing the head, tail, viscera, bloody colored flesh and skin portions therefrom, crushing the remaining edible portions to obtain flakes, seasoning them and if desired adding edible oil thereto. The yield of those raw fish to be used, however, tend to be up and down based on variable conditions concerning ocean currents, weather and the like. In addition, the reduction in yields and sudden rise in prices of the raw fish such as tuna and bonito have resulted from the current legislation in many countries for laying claim to their 200 miles territorial waters. Accordingly, the manufacturers of the canned foods of fish flakes recently find it difficult to obtain those raw fish in a stabilized amount and price. In this situation, new merits of vegetable proteins were discovered in their usage in place of fish flakes and revaluated in agreement with consumer's preference for healthy foods.
Vegetable proteins, in particular the granulated soya protein prepared by extrusion process, have meat-like structure and taste. When the extruding conditions are chosen, the layered soya protein may be obtained and available for the preparation of soya protein flakes by means of a suitable apparatus. However, thus prepared soya protein flakes are utterly different in their structure and taste from the fish flakes. Therefore, this sort of soya protein flakes cannot substitute for the fish flakes.
U.S. Pat. No. 3,870,805 discloses a method for producing soya proteins having similar taste to chicken, clam, lobster or the like by using a couple of dies standing abreast. The couple of dies enables the formation of fibrous structure of the protein which has muscular taste stronger than the protein extrudate by means of a single die. The thus obtained muscular taste can remain even after the fibrous protein is subjected to retort heating at 240.degree. F. for 30 min. However, this soya protein having muscular taste is far different in its structure and taste from the fish flakes and can hardly substitute therefor.